We have often been told that eating junk food is ok if it is done in moderation. However, a new study has found that eating even one junk food meal that is high in saturated fat can damage our arteries.

Canadian scientists set out to compare the effects of a junk food meal and a Mediterranean meal on the vascular endothelium - the inner lining of the blood vessels. Problems in this area are known to increase the risk of developing coronary artery disease.

The study involved 28 men, who were all non-smokers. Each was assessed before and after being fed a Mediterranean meal. They underwent the same assessments a week later when fed a junk food meal.

A Mediterranean diet involves a high intake of olive oil, fruit, vegetables, nuts, seeds, fish and starchy foods such as red potatoes and pasta. Dairy products, poultry and wine are consumed in low to moderate amounts, while red meat is rarely eaten.

In this case, the Mediterranean meal was composed of salmon, vegetables and almonds cooked in olive oil. While just over half the total calories came from fat, these were considered ‘good' fats, such as polyunsaturated fats.

The junk food meal was a sausage, egg and cheese sandwich, accompanied by three hash browns. Just over half of the calories also came from fat in this meal, however, these were mainly saturated fatty acids.

The scientists found that after consuming the junk food, the men's arteries dilated 24% less than they did if the men were fasting. This poorer dilation can adversely affect blood flow. This shows that just one meal high in saturated fats has a detrimental effect on the arteries.

However, after eating the Mediterranean meal, the arteries dilated normally and good blood flow was maintained.

Furthermore, those with high triglyceride levels had an even better response to the Mediterranean meal than those with low levels. Triglycerides are a type of blood fat, which are often found in people with high levels of ‘bad' cholesterol.

According to the scientists, these findings ‘will positively alter how we eat on a daily basis'.

Poor endothelial function is one of the most significant precursors of atherosclerosis (hardening of the arteries). It is now something to think about at every meal," they said.

Details were presented at the Canadian Cardiovascular Congress in Toronto.